1. Field of the Invention
The present invention concerns a method for magnetic resonance imaging using a partial parallel acquisition technique with non-Cartesian occupation of k-space, with a number of antennas disposed around an imaging volume for reception of magnetic resonance signals, and with spatial coding of the magnetic resonance signals in the imaging volume by means of magnetic gradient fields such that k-space is only incompletely occupied with magnetic resonance signals, with at least one trajectory proceeding around the origin of k-space.
2. Description of the Prior Art
A method of the above-described type is known from the article by Pruessmanet al. “Advances in Sensitivity Encoding with Arbitrary k-Space Trajectories”, in Magnetic Resonance in Medicine, Vol. 46, pages 638-651, 2001. For magnetic resonance imaging using a partial parallel acquisition technique, the reception signals from a number of antennas disposed around an examination volume are further processed into a image of the imaging volume that is free of aliasing artifacts. In the SENSE method, an aliasing-free reconstruction ensues from individual images of the reception antennas, even though the individual images themselves exhibit aliasing foldings. This is accomplished by k-space not being occupied by the reception signals of the individual antennas, i.e., it is under-scanned. The method specified in the artifacts for reconstruction that is free of aliasing artifacts allows k-space to be occupied with the reception signals along arbitrary trajectories, in particular along spiral trajectories. Spiral trajectories are used in neuro-imaging and cardio-imaging. The k-space trajectories are determined by the magnetic gradient fields used for spatial coding. The reconstruction effort, however, is computationally intensive in this known method.
Because of the non-Cartesian k-space occupation, the artifact behavior is reduced. For example, artifacts known as “blurring” artifacts and fluctuations of physiological parameters (physiological noise) are thereby reduced. This method is additionally less susceptible to deficiencies of the apparatus (such as, for example, inhomogeneities).
A method involving a different partial parallel imaging technique is know from German OS 101 26 078. In that method (as in the SENSE technique) reception signals are acquired by a number of antennas and are sorted into respective k-space associated with the antennas. The k-spaces are again incompletely occupied. In contrast to the SENSE method, however, missing sample points in each scanned k-space are determined from existing sample values with usage of a previously-determined weighting matrix. Such methods belong to the SMASH family and are known under the designations SMASH, AUTO-SMASH, VD-AUTO-SMASH and GRAPPA. Partial images that are then processed into an overall image of the imaging volume are then generated from completed k-spaces of the individual antenna signals by means of respective Fourier transformations. The method is described for a Cartesian occupation of k-space.